1. Field of the Invention
The present invention relates to metallized plastic moldings in which a plastic substrate is coated with a primer layer and then a metallic film layer is deposited on the primer layer and to a method for producing the same.
2. Description of the Prior Art
In the past, metallized plastic moldings composed of a plastic substrate wherein one of the surfaces of the substrate has been subjected to metallizing treatment have been used for various decorative articles, mirrors, and the like. The structures have been used because of such advantages as high productivity, good moldability, light weight, and the like, which are characteristic properties of plastics. Plastic substrates have been metallized in the past by plating methods, hot-stamping methods, vacuum evaporation methods, sputtering methods, ionizing plating methods and the like. Among these techniques the plating method is most commonly used. The plating method involves subjecting the surface of a plastic substrate to chemical plating and then to electroplating. However, the steps of this method are complicated and an additional problem is the necessity of disposing of toxic waste plating solutions and the high cost of disposing of the solutions. For this reason, it would be highly desirable to have a method of metallizing plastic moldings which is simple and which presents no aqueous waste liquor disposal problems as a substitute for the plating method. For this reason such dry methods of forming metallic films as vacuum evaporation, sputtering, and the like have been considered. Although plastic moldings having a metallic gloss can be prepared by these dry methods, the metallic film layers formed by these methods are extremely thin and are not very adhesive to the plastic substrate. Consequently, the resulting products exhibit substantially inferior properties such as abrasion resistance and weather resistance. A recent method which has been proposed to increase the strength of the metallic film layer formed by the dry metallic film forming methods involves the coating of a plastic substrate with various primer materials such as a composition of acrylpolyol and polyisocyanate on the surface of a plastic substrate, heat treating the coated substrate to form a primer layer and then forming a metallic film layer thereon by a dry metallic film forming method. This method has provided considerably good results. However, the metallized plastic moldings obtained by this technique exhibit low adhesivity between the primer layer and the metallic film layer and as a result the metallized substrates do not exhibit abrasion resistance and weather resistance properties. During the formation of the metallic film layer or during the use of the metallized plastic moldings, especially in outdoor use, the metallized products develop haze, whiten, cracks develop and the rainbow phenomenon occurs in the metallic film layer and accordingly these products are not practically useful. A need, therefore, continues to exist for a dry method of metallizing plastic substrates to form a product in which there is substantial adhesivity between plastic substrate and metal layer.